The foundation weighed many factors, Mr. DiGiovanni said, among them the risk of the animal injuring itself in the process of being captured; the daunting logistics (including federal permission) and lead time required for safely removing a dolphin from water; the very low survival rate, under 10 percent, of dolphins that are taken in for rehabilitation; and, yes, the possible danger to staff members of exposure to the canal’s toxic goo, the subject of a $500 million Superfund cleanup.